Fuse actuator switch



Nov. 4, 1969 RAMHALL E 3,477,054

FUSE ACTUATOR SWITCH Filed 001;. 2, 1967 2 Sheets-Sheet '1 FiG.2

32g 74 as 2 g 629 78 34Q' 124 FFG. 4

INVENTORS. OTIS H; BRAMHALL BY THURMAN S. JESS ATTORNEY Nov. 4, 1969 BRAMH ETAL 3,477,054

FUSE ACTUATOR SWITCH Filed Oct- 2, 1967 2 Sheets-Sheet z ill 98 4! INVENTORS. OTIS H. BRAMHALL THURMAN s. JESS ATTORNEY United States Patent U.S. Cl. 337-202 Claims ABSTRACT OF THE DISCLOSURE A thermally actuated switch having both a fixed contact and a movable contact, the movable contact being held under tension by a fusible means. The fusible means separate at a predetermined current level releasing the movable contact relative to the fixed contact to either make or break a circuit.

BACKGROUND OF THE INVENTION Early thermal responsive relays utilized mercury as an actuating medium.

In cases where a blown fuse indicator was needed, a fuse element was attached to a spring loaded element whereby breaking of the fuse element released the spring loaded element which, in turn, actuated a switch to turn on a light or other warning device.

There are presently available on the market, current sensitive relays which include a spring loaded plunger con tact held in that condition by a fuse Wire. The fuse wire is set to melt at a specific amperage releasing the plunger contact to engage a pair of terminals or to disengage from a pair of terminals either opening or closing a circuit.

SUMMARY OF THE INVENTION This invention is directed at a fuse actuated switch provided with a fixed contact and a movable contact, the latter being held from, or with, the former under spring tension by a fuse wire. In operation, the fuse wire at a predetermined amperage will release the movable contact and thereby either make or break a circuit.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a fuse actuated switch with the cover removed and partly in section.

FIG. 2 is a bottom plan view of the switch shown in FIGURE 1 with the cover removed and partly in section.

FIG. 3 is a top plan view of a variation of the switch shown in FIGURE 1 with the cover removed and partly in section.

FIG. 4 is a section taken on line 4-4 of FIGURE 3.

FIG. 5 is an end elevation of the fuse insulator of the switch shown in FIGURE 3.

FIG. 6 is an end elevation of the contact engagement portion of the switch shown in FIGURE 3.

FIG. 7 is a section taken on line 77 of FIGURE 6.

FIG. 8 is an end elevation taken from the opposite end of the contact engagement portion shown in FIGURE 7, and

FIG. 9 is a top plan view of the terminal portion of the switch shown in FIGURE 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, there is shown a fuse insulator 10 gen erally cylindrical in construction, having a spring retainer groove 12 formed from end to end thereof and having a terminal end 14 chamfered in the direction away from the direction toward which the groove 12 opens. On the 3,477,054 Patented Nov. 4, 1969 opposite side of the fuse insulator 10 from the groove 12 a lead slot 16 is formed opening at the terminal end opposite to the end 14 and having a rib 18 extending along its mid-line providing two shallow compartments. A protuberance 20 extends from the fuse insulator 10 between the terminal ends 14 and the lead slot 16. A step 22 is formed in close proximity to the end 14 and transverse the spring retainer groove 12 to provide a space for the yoke 38 and spring contact 32 and also to help in aligning the switch insulator 24 which will be more fully described hereinafter.

The adapter terminal assembly comprises a glass seal 26 generally circular in configuration circumscribed by an eyelet with a flange extending therefrom and three tubes extending axially therethrough. The eyelet of the glass seal 26 is circumscribed in abutting relationship by an adaptor sleeve 28 made of a conductive material such as brass.

The leads 30 extend through two of the tubes of the glass seal 26 and each of them lies within a compartment of the lead slot 16. Each of the leads 30 are soldered into their respective tubes. The flexible wire spring contact 32 is soldered to the third tube of the glass seal 26 and extends along and beyond the spring retainer groove 12.

An insulator sleeve 34 is slipped around the contact 32.

A wire fuse element 36 formed of an electrically conducting material which will melt at a predetermined temperature or at a predetermined electrical current level, is soldered to the terminal ends of the leads 30 and lies within the lead slot 16, providing a loop which extends beyond the protuberance 20. The wire fuse element is placed under a fixed amount of tensile force to be more fully described hereinafter.

The yoke 38 comprising a loop of flexible wire having each of its free ends bent to provide arcuate engagement portions 40 is engaged to the fuse assembly placing the bight of the yoke 38 against the insulating sleeve 34 which surrounds the spring contact 32 flexing the spring contact 32 against the bottom of the spring retainer groove 12. While the spring contact 32 is in this fixed and tensioned position the loop of the wire fuse element 36 is engaged with the arcuate engagement portions 40 completing the assembly.

The relationship of the wire diameter of the yoke 38 and the wire fuse element 36 is important. The yoke 38 material diameter should be larger than the diameter of the wire fuse element 36 material. If it is too small when the fuse wire breaks, the remaining portion of the fuse wire would be unable to slip freely around the yoke thereby causing the yoke 38 and spring contact 32 to hang up and not operate properly.

The switch portion of the electrical assembly comprises the switch insulator 24 which is tubular in outer configuration and has a front face 44 provided with a longitudinal slot 46 which acts as a guide for the spring contact 32 and also lines up the free terminal end of the spring arm with contact lead wires 48. The dimensions of the slot 46 are such as to prevent excessive lateral movement of the spring arm under shock or vibration. A tongue 50 extends from the bottom of the front face 44 and has the form of a section of a cylinder. The rear face 52 of the switch insulator 24 is provided with a keyed aperture 54 which will accept the lead Wires 48 in two different positions, as will be more fully explained hereinafter. The switch contact subassembly includes a flanged grommet 66 having an electrically insulating seal 58 which has tubes formed therein through which the lead wires 48 are bent at an angle to engage the end of the spring contact 32 in a closed circuit position or the switch contact subassembly may be turned so that the lead contacts 48 are bent away from the contact spring 32 in an open circuit position.

To engage the switch portion with the fuse or actuator portion of the assembly, an outer tubular housing element 62 formed of metal is slipped over the fuse assembly, with an insulating sleeve portion 64 lining the interior of the tubular housing element, and is then soldered in place as shown in FIGURE 1, to make a hermetic seal. The switch assembly is then slid within the housing element 62 with the tongue 40 engaging the step 22 of the fuse insulator 10. The contact lead wires 48 will either be engaged with the Wire spring contact 32 if a normally closed switch is desired 'or will be turned 180 to provide a normally open switch. The housing element 62 is now soldered to the flange of the grommet 66 to complete the total hermetic construction. It is somethings necessary that a spacer 28a similar to the adapter sleeve 28 be used between the housing element 62 and the grommet 66.

When a current flows through one of the leads 30, its path would be through the wire fuse element 36 and out the other lead 30 for whatever purpose is desired such as a tie-in with a sensitive instrument, or to provide a trigger for an electrical circuit at a predetermined current. The inventors use an 80% nickel, 20% chrome wire of .005" diameter which will melt or separate at 1% amps of current in one second and is rated to carry /2 amp of current continuously without actuating the switch circuit within required design parameters.

If the switch end is normally closed, there will also be a circuit through the contact lead wires 48 and the terminal end of the wire spring contact 32. When the Wire fuse element 36 separates, the wire spring contact 32 will move away from the contact lead wires 48 opening the circuit. This operation will be reversed if the switch end is normally open. Note that once the wire fuse element 36 has blown and the switch is actuated, that the function cannot be reversed.

The variation shown in FIGURES 3 and 4 differs from the original construction in that the leads 3011 are sealed directly in the glass without the use of tubes. The wire spring contact 32a is engaged to the glass seal 26a through the use of a blind tube 70 as shown in FIGURE 4. The use of the blind tube 70 assures, since there is no opening to the outside, that the seal is hermetic.

The yoke 38a comprises a shank portion having a large hook 74 formed at one end, a smaller hook 76 formed at the other end which lies on a plane normal to the plane of the hook 74. The bight of the wire fuse element 36a is engaged around the small hook 76 while the large hook 74 is engaged around the wire spring contact 32a.

The fuse insulator a is generally tubular in configuration and has a spring retainer tunnel 78 formed through it from end to end along the lower level as shown in FIG- URES 4 and 5. The spring retainer tunnel 78 has the general configuration of a truncated ellipse and is completely enclosed on the bottom. A lead cavity 96 is formed for approximately one-third the length of the fuse insulator 10a, open at the-top, and having an aperture 90 formed on its floor, opening into the spring retainer tunnel 78 as shown in FIGURE 4. The fuse insulator 10a has a raised portion which has its upper surface on a plane above that of the floor of the lead cavity 96 and has a rectangular protuberance a, extending from its midline upwardly away from the spring retainer tunnel 78 to maintain centering of the fuse insulator 10a, by having its upper surface butted against the housing element 62a, when the switch is assembled. The upper surface of the raised portion is slanted upwardly from the lead cavity 96 and terminates in an inclined forward wall 86 which provides surfaces on which the large hook 74 of the yoke 38a rests when the switch is assembled. The spring retainer tunnel 78 divides the forward wall 86 into two surfaces which are continued as shown in FIGURE 5 as two shelves 98 along the side walls of the fuse insulator 1011. A pair of spaced semicircular keys 80 extend from the terminal end of the fuse insulator 10a, and have an outer surface which conforms to the outer surface of the fuse insulator 10a. The shelves 98 and the bottom of the fuse insulator 10a, define a narrow portion of a cavity 82 which occupies the end of the fuse insulator 10a, from the forward wall 86. The spring retainer tunnel 78 opens into the cavity 82 as shown in FIG- URES 4 and 6. At the upper portion of the forward wall 86 a transverse bearing pin groove 88 is formed which passes through each side Wall of the fuse insulator 10a. A cylindrical bearing pin 94, formed of a tough material, is engaged in the bearing pin groove 88.

The switch insulator 24a comprises a contact engagement portion and a terminal portion 102. Contact engagement portion 100 is tubular in configuration and has a contact cavity 104 in the general shape of a cross forme which is closed off at one terminal end by a base portion 106. The base portion 106 has a slot 108 formed through it and a pair of spaced arced slots 110 formed on its edge to accept the keys 80 of the fuse insulator 10a. An upper shoulder portion 112 and a pair of spaced lower shoulder portions 114 extend from the base portion 106 as shown in FIGURES. 7 and 8, for a purpose to be set forth hereinafter. vA pair of spaced arced slots 116 are formed on the edge of the contact engagement portion 100 at its lower portion as shown in FIGURE 8 remote from the base portion 106.

The terminal portion 102 is generally cylindrical in configuration having a rectangular slot or trough 118 formed centrally in the plane surface. The base of the terminal 102 is pierced by a pair of spaced terminal apertures 120 which open into the rectangular slot 118. The rectangular slot 118 is arced at its top and bottom wall surfaces and its side walls are angled to define with the top and bottom walls what may be referred to as a truncated trianglepA pair of spaced key portions 122 extend from the edge of the plane surface as shown in FIGURE 10.

The contracts 124, formed of a conductive material, such as copper comprise a flat contact portion 126 which is slightly bowed and which has a spring leg 128 extending from an edge at a central portion of the contact portion 126. The spring leg 128 is bent back on itself to provide a major portion spaced from the contact portion 126 and providing a generally T-shaped configuration therewith. The fuse element subassembly comprising the leads 30a, thewire spring contact 32a, the looped wire fused element 36a, which is soldered or otherwise fastened at its terminal ends to the leads 30a, as shown in FIGURE 3, the glass seal 26a formed inside the flanged eyelet with the parts assembled as set forth hereinbefore.

To assemble the switch, the fuse element subassembly with the wire spring contact 3201, is connected to the fuse insulator 10a, by passing the wire spring contact 32a, into the spring retainer tunnel 78 while simultaneously placing the loop of the wire fuse element 36a around the protuberance 20a, and butting the flanged eyelet against the terminal end of the fuse insulator 10a as shown in FIGURES 3 and 4. An insulator sleeve 34a is placed around the wire fuse contact 32a, either before assembly with the fuse insulator 10a, or after such assembly. The yoke 38a is engaged to the assembly'by looping the smaller hook 76 around the bight of the wire fuse element 36a and looping the large hook 74 around the insulator sleeve 34a with the large hook 74 abutted against the forward wall 86. The bearing pin 94 formed of a tough material is now driven into the bearing pin groove 88 after the wire spring contact 32a is flexed upwardly, placing it under spring tension. Since the bearing pin 94 presses against the yoke 38a the wire spring contact 32a will be maintained in a flexed or stressed position and will not become imbedded in the relatively soft plastic forward wall 86.

The contacts 124 are assembled with the contact engagement portion 100 by dropping their bight portions into the contact cavity 104 with the terminal ends of the contact portion fitted into longitudinal slots 130 as shown in FIGURE 8. The slots 130 are so arranged that the contact portions 126 of the contacts 124 form angles with the longitudinal midline of the contact engaging portion 100. The assembled contact portions 126 define an open V construction. The free terminal ends of the spring legs 128 extend beyond the end of the contact portion 126.

The contact engagement portion 100 with its contacts 124 is assembled with the fuse insulator assembly by passing the end of the wire spring contact 320, through the slot 108 in the base portion 106 to engage the. hearing surfaces of the contact portions 126 proximate the apex of the open V. The keys 80 of the fuse insulator a, are engaged in their proper arced slots 110 in the contact engagement portion 100 butting the base portion 106 against the terminal end of the fuse insulator 10a. If we turn the contact engagement portion 100 around 180 we provide a normally open switch construction rather than the normally closed construction described hereinbefore. Behind the protuberance 20a and aperture 90 is formed through the upper wall of the spring retainer tunnel 78. A double sided cam 92 having a shank portion fitted into the aperture 90 lies between the two leads 30a. To increase the amount of tension between the leads 3011 the yoke 38a and the wire fuse element 36a, the double sided cam 92 is turned camming the leads 30a away from each other and thereby increasing the tension on the wire fuse element 36a and the yoke 38a. When the tension reaches a satisfactory or sufiicient level, the cam 92 is fixed in position using an adhesive or other appropriate means.

The variation operates substantially in the same way as the switch disclosed in FIGURES 1 and 2 as described in column 1 thereof. 7

With reference to the foregoing description it is to be understood that what has been disclosed herein represents several embodiments of the invention and is to be construed as illustrative rather than restrictive in nature and that the invention is best described by the following claims:

1. A thermal relay comprising a housing, a resilient movable contact mounted within said housing, and at least one fixed contact, the housing having a longitudinal channel within which a portion of the movable contact lies, the movable contact being fixedly held at one end by the housing and having its other end held under fiexure by a yoke formed of nonfusible material, said yoke being engaged to a heat fusible material which will fuse when a predetermined electric current is passed therethrough thereby releasing the flexible movable contact which changes its position relative to the fixed contact to either make or break a circuit.

2. A thermal relay as set forth in claim 1 wherein said fusable material is in the form of a looped wire having terminal ends each of which is attached to a lead wire.

3. A thermal relay as set forth in claim 2 wherein said housing includes a switch insulator portion adapted to be turned degrees in relation to the remaining portion of said housing, whereby said relay may be changed from one which is normally opened, to one which is normally closed.

4. A thermal relay as set forth in claim 2 wherein said housing includes a means of flexing said leads away from each other and thereby increasing the tension on said movable contact.

5. A thermal relay as set forth in claim 4 wherein said yoke is looped about said fusable wire and about said movable contact, and abuts a surface within said housing which is in angular relation to the plane of the axis of the housing.

References Cited UNITED STATES PATENTS 2,356,352 8/1944 Pittman 337- X 2,518,909 8/ 1950 Krakauer 337-190 X 2,757,259 7/1956 Cruse 337-178 X 2,769,059 10/ 1956 Baenziger 337-290 X 2,913,555 11/ 1959 McAlister 337-164 3,155,800 11/1964 Denton 337-409 3,264,438 8/1966 Gay 337-403 BERNARD A. GILHEANY, Primary Examiner H. B. GILSON, Assistant Examiner U.S. Cl. X.R. 337-190 

